In order to cut to length extruded tubes, what are known as flying saws are usually used, a circular saw blade being brought towards the tube to be sawed from below (underfloor saw), from above (plunge saw), or from the side (crosscut saw), plunging into the cross section of the tube, and cutting through the wall thickness in a first step. In a second step, the saw blade is guided around the tube in order to fully cut the tube to length. In this case, the tube that is to be cut to length is clamped during the sawing process. The saw carriage then moves at the extrusion speed synchronously with the continuously progressing extrusion process (“flying saw”).
When tubes are sawed, sawdust is produced. In addition, a static charge is generated due to the friction of the saw blade on the tube, in particular in the case of a plastics tube. This is disadvantageous in that the sawdust adheres to the tube, resulting in contamination. The waste material produced often has to be declared as hazardous waste, meaning that it cannot be recycled.
A device in which tubes are cut to length in a chipless manner is already used for small tubes. Rather than a running saw, a round knife is guided around the tube until the tube wall has been cut through.
The chipless cutting just mentioned makes it possible to cleanly cut small tube diameters having a thin cross section, but it has hitherto not been successful in also cutting to length thick-walled tubes having large or very large diameters, i.e. diameters of approximately 2 m. For these tubes, recourse is always made to the saws mentioned further up, resulting in the known disadvantages.
Tests have shown that the main problem lies in precisely guiding the knives through the thick-walled tube. On account of the large thickness and the large diameter, even at the smallest inclination of the knife said knife is canted in the material, which results in the knife breaking.
For cutting units of this kind, the market requirements are for a high linear speed at short cutting lengths and the option of applying a chamfer, for example in sewage pipes made of PP/PVC. Although automatic cutting machines are known that can carry out the cutting process very rapidly, said machines usually have the disadvantage that they cannot produce chamfers or that they are not suitable for all types of plastics material. However, automatic cutting machines which can produce chamfers usually have a comparatively large saw carriage and are therefore slow. The time required to make a cut is thus very long.
In the current machines such as saws (flying saws), tubes having a wide range of diameters are cut through by a cutting knife arm or a saw arm moving around the tube. All the functions necessary for this purpose, such as moving the arm forward and back, clamping/releasing the tube, and the corresponding position feedback are installed on the disc rotating about the tube. For this purpose, slip rings are used for the electrical signals. The usual procedure is to use a dedicated slip ring channel for each signal respectively. The signals, and thus the available functions, are limited by the structural size in smaller machines and by the cost per slip ring.
A solution to the above-described problem is disclosed in DE 20 104 200, but does not yet provide satisfactory solutions.